A fermentation production process of a chemical substance from sugar as a raw material has been used in production of various industrial raw materials. Recently, as sugar used as a fermentation raw material, a substance derived from an edible raw material such as sugarcane, starch, and sugar beets has been industrially used. However, the edible raw material may be insufficient due to an increase in the global population in the future, and this may cause a sudden rise in prices. Therefore, development of a process to efficiently produce a sugar solution from a renewable inedible material, that is, cellulosic biomass has become an issue.
Cellulosic biomass mainly includes lignin that is an aromatic polymer, and cellulose and hemicellulose that each are a monosaccharide polymer. Examples of a method of producing a sugar solution from cellulosic biomass as a raw material may include a method of directly hydrolyzing cellulosic biomass as a raw material using concentrated sulfuric acid or the like, and a pretreatment-enzymatic saccharification method in which cellulosic biomass is subjected to a pretreatment such as a steam treatment, a fine pulverization treatment, and a treatment with dilute sulfuric acid in advance, to separate cellulose and hemicellulose from lignin, and cellulose and hemicellulose are hydrolyzed with a diastatic enzyme such as cellulase.
A sugar solution produced from cellulosic biomass obtained by these methods has a problem in which during a process of producing the sugar solution, a fermentation inhibitor such as hydroxymethyl furfural (HMF), furfural, and vanillin is produced and, during production of alcohol and the like by fermentation of the obtained sugar solution, fermentation of the sugar solution is inhibited. Further, the sugar concentration of a sugar solution to be obtained may be low depending on treatment conditions of production of the sugar solution. In that case, the sugar solution needs to be concentrated several times to about 10 times before the fermentation step. As a method of removing the fermentation inhibitor in the sugar solution and at the same time, increasing the sugar concentration during production of the sugar solution from the cellulosic biomass as the raw material, a method of treating the sugar solution using a nano-filtration membrane has been disclosed (for example, see International Publication Nos. 2009/110374 and 2010/067785).
In general, the pretreatment-enzymatic saccharification method has such an advantage that the environmental impact is smaller as compared with the method of directly hydrolyzing the raw material, but on the other hand, the sugar yield is low. As a pretreatment method in which the environmental impact is small and high sugar yield is obtained, a pretreatment method using a treatment agent containing ammonia has been proposed (for example, see Japanese Laid-open Patent Publication No. 2008-161125).
In general, in a sugar solution obtained from cellulosic biomass subjected to a pretreatment such as a steam treatment, as described above, a fermentation inhibitor such as hydroxymethyl furfural (HMF), furfural, and vanillin is produced during a process of producing the sugar solution, and fermentation of the sugar solution is inhibited during production of alcohol and the like by fermentation of the obtained sugar solution.
On the other hand, in a sugar solution obtained by the pretreatment-enzymatic saccharification method using the pretreatment with a treatment agent containing ammonia as described in JP '125, the above-described known fermentation inhibitor is hardly detected, but it is found that fermentation of the sugar solution is inhibited like a sugar solution obtained using cellulosic biomass.
Therefore, it could be helpful to provide a method of producing a sugar solution capable of improving the fermentation efficiency of the sugar solution during fermentation of the sugar solution obtained using cellulosic biomass pretreated with a treatment agent containing ammonia that can achieve high sugar yield to aim at improving the production efficiency of ethanol and the like using the sugar solution obtained from cellulosic biomass, as well as to provide a sugar solution and a method of producing ethanol.